Disproportionation of xylenes



INVENTORS: Arthur P Lien David )4. McCau/ay Altar/7e) A. P. LIEN ETALFiled Aug. 25, 1948 DI'SPROPORTIONATION OF XYLENES Aug. 14, 1951 wcmax 8Patented Aug. 14, 1951 DISPROPORTIONATION OF XYLENES Arthur P. Lien,Hammond, Ind., and David A. McCaulay, Chicago, Ill., assignors toStandard Oil Company, Chicago, 111., a corporation of IndianaApplication August 25, 1948, Su ial No. 46,135

1'7 Claims. (Cl. 260-672) This invention relates to a process for thedisproportionation of xylenes. More particularly, it relates to thedisproportionation of a xylene, particularly meta-xylene, in thepresence of catalysts consisting essentially of liquid hydrogen fluorideand BFa. By the process of this invention, mesitylene and toluene can bereadily produced in concentrated form by a commercially practicablesequence of operations. The process of this invention also renderspossible the conversion of a meta-xylene concentrate to orthoandparaxylene concentrates, toluene and mesitylene.

Although the disproportionation of xylenes has been extensively studied,no process of commercial significance has thus far been developed. Theprincipal catalysts heretofore studied have been Friedel-Crafts typemetal halides, particularly aluminum chloride. The prior art processesfor the disproportionation of xylenes have been handicapped by largecatalyst requirements and consumption, tar and sludge formation,inability to regenerate the metal halide catalysts which wer employedand the relatively low yields of mesitylene and high yields of unwantedtrimethylbenzenes, viz., 1,2,3- and particularly 1,2,4-trimethylbenzeneswhich were obtained. In contrast, by the process hereinafter detailed,xylenes can be disproportionated in essentially quantitative yield toproduce toluene and a highly concentrated mesitylene product.

There is a large unsatisfied commercial demand for polycarboxylic acids,particularly aromatic polycarboxylic acids, forthe production of alkydtype resins and plastics. It is possible to oxidize mesitylene to thecorresponding 1,3,5- benzene tricarboxylic acid which would be valuablefor the above mentioned uses. Another very valuable use of mesitylene isas a component of premium high octane fuels. Of all the hydrocarbonstested thus far, mesitylene is among the highest in clear CFR-R octanenumber. It has the highest blending octane number of any purehydrocarbon tested thus far. A comparison of the octane number ofmesitylene with other aromatic hydrocarbons is shown in the followingThe blendin octane numbers were obtained on blends of 20 percent of thearomatic hydrocarbon with 80% of a octane number standard referencefuel. It will be apparent that the conversion of any of the xylenes tomesitylene results in a significant octane number increase, which isespecially noteworthy in the case of ortho-xylene which has the lowestblending octane number. It should also be noted that mesitylene isisomeric with cumene which was extensively used as a high octane numberaviation gasoline component, has similar physical properties, e. g.,volatility characteristics, and would thus be a valuable constituent ofsafety fuels.

In our process, a xylene concentrate, comprising any one of the isomericxylenes or a mixture thereof, e. g., hydroformate xylene, iscontactedwith a catalyst comprising HF plus BFa. Suitable conditions forthe conversion are temperatures of about 200 F. to about 600 F.,preferably about 250 F. to about 350 F., amounts of HF between about 3and about 20 mols per mol of xylene feed, and amounts of BF: betweenabout 0.01 and about 3 mols per mol of xylene. Suflicient reaction timeis allowed to afford substantial disproportionation, e. g., betweenabout 2 minutes and about 4 hours.

It is preferred to employ a reaction mixture containing at least 0.5 molof BE; per mol of xylene charging stock, e. g., between about 0.5 andabout 3 mols of BF; per mol of xylenes. The presence, in the reactionmixture, of at least 0.5 mol of BF; per mol of xylenes results, inefiect, in the segregation of the mesitylene produced in the reaction asa complex with HF and BF: containing one mol of BF: per mol ofmesitylene. A further advantage of high BF: concentration is thatmesitylene is the predominant C9 aromatic produced in thedisproportionation reaction.

The reaction may b carried out in a batch type reactor equipped withmechanical agitation, or in a tower type reactor. The reaction productsmay be subjected to stripping action to completely separate the HF andBF'a; the hydrocarbons are thereafter fractionated to separate a toluenestream, a xylene stream for recycle to the process, and a mesitylenestream. In one modification of our process, only a portion of the BF: isflashed ofi, preferably about one mol of BF3 being retained per mol ofmesitylene in the product, whereupon by cooling to ambient temperature,a, diphasic separation is obtained, mesitylene being concentrated as thelower HF-BF: complex, the bulk of the toluene and xylene being separatedas rafilnate.

The toluene produced by this process is of high purity and can benitrated directly.

Analysis of unconverted xylenes derived from the process of thisinvention indicates that considerable xylenes isomerization has occurredconcurrent with-or prior to the xylenes disproportionation reaction.Surprisingly, the trimethylbenz'enes produced by xylenedisproportionation in the process of our invention consist almost whollyof mesitylene with small proportions of the order of 10 percent or evenless of pseudoumene (1,2.4-trimeth'ylbenzene). The high mesityleneconcentration of our product is all the more surprising in view of thefact that it is far in excess of the amount which would be expected fromthermodynamic equilibrium data (Wm. J. Taylor et al., Heats, EquilibriumConstants, and Free Energies of Formation of the Alkylbenzenes ThroughCal-I12 and of the Higher Normal Monoalkylbenzenes, presented before thePetroleum Division, American Chemical Society, April 8-12, 1946, FigureThe formation of mesitylene in such unexpectedly high concentration isbelieved to be attributable in some measure to the formation of acomplex between mesitylene, BF: and HF; it is probably also due in somemeasure to the isomerization of any mesitylene isomers that might beproduced in the course of the xylenes disproportionation reaction.

The disproportionation of xylenes in the presence of liquid hydrogenfluoride and BF3 is a surprisingly clean cut, smooth reaction. Nohydrocarbons other than toluene, xylenes and trimethylbenzenes have beenobserved by us in the disproportionation reaction products. Thisindicates that the more extensive and random disproportionationreactions encountered previously when aluminium chloride was employed asa catalyst are not encountered here. In addition to the products that wehave observed by the operation of our process, aluminum chloride alsoyields some benzene, tetramethylbenzenes such as durene, and even highermolecular weight products.

When liquid hydrogen fluoride alone is employed as a catalyst for thedisproportionation of xylenes. the principal trimethylbenzene reactionproduct is pseudocumene. Also, the amount of polymethylbenzenes ofhigher molecular weight than trimethylbenzenes produced by the use ofliquid HIF as the catalyst is often equal to and, in many instances,even greater than the amount of trimethylbenzenes produced. By theemployment of BF: with liquid hydrogen fluoride, we have found itpossible. first, to suppress disproportionation and condensationreactions which proceed to form products of higher molecular weight thantrimethylbenzenes and, secondly, to produce mesitylene, predominantly,as the C9 aromatic hydrocarbon product. Both of these results areentirely unexpected in view of the action of liquid hydrogen fluoridewhen employed alone as a catalyst for the disproportionation.

Whereas it appears that mesitylene is preferentially dissolved by liquidhydrogen fluoride and BFa. the other xylene disproportionation product,viz., toluene, is not.

The disproportionation-extraction process of our invention findssuitable application in the treatment of individual xylene isomers,mixtures of any two or all three xylenes and in the treatment of xylenemixtures containing ethylbcnzene and/or saturated hydrocarbons of closeboiling range. The boiling points and freezing points of the xylenes,and of ethylbenzene which boils within the same range, are

("Selected Values of Properties of Hydrocarbons," Nat. Bur. Stds., 0461,November 1947, p. 67.)

Aromatic hydrocarbon charging stocks suitable for employment as feedstocks in the process of this invention can be prepared by a variety ofprocesses, probably the most important of which is the catalytichydroforming process. For the preparation of xylene-rich products, adesirable charge to hydroforming is a light naphthenic naphtha rich indimethylcyclohexanes (boiling range about 230 to 280 F). In this processa petroleum naphtha, which may be a virgin or cracked naphtha or mixtureof both, is converted to aromatic hydrocarbons by contact with a solid,porous dehydrogenation catalyst at a temperature in the range of about850 F. to about 1050' F., preferably in the presence of hydrogen.Suitable catalysts are oxides of metals of groups 2 to 6 of the periodicsystem, particularly oxides of 6th group metals such as chromium andmolybdenum, preferably supported by alumina or magnesia. Excellentcatalysts can be prepared by depositing about 4 to about 10% ofmolybdenum oxide upon an activated alumina. Suitable space velocitiesfor hydroforming fall within the range of about 0.2 to about 4 volumesof the liquid charge per hour per volume of catalyst space. About 0.5 toabout 8 mols of hydrogen can be charged to the process with each mol ofnaphtha feed stock. (Note also, G. Armistead, Jr., Oil and Gas, J. 45,17 (August 31, 1946) pp. -7 and L. R. Hill et al., Trans. Am. Inst.Chem. Eng. 42, 4 (August 25, 1946) pp. 611-637).

Other sources of xylenes and other aromatic hydrocarbon charging stocksfor employment in our process are catalytic cracking, catalyticdehydrogenation of naphthenes over dehydrogenation catalysts such asNiSWSz or the like, thermal cracking at high temperatures, preferably inthe presence of steam, for example as in the Forward process; theextraction or extractive distillation of virgin naphthas and kercseneswith selective solvents such as phenol, methanol, ethylene glycol,furfural, S02 and the Lice; the coking of coal, which yields a lightaromatic oil from which it is conventional practice to produce nitrationgrade xylenes, etc. The above-mentioned processes for the preparation ofaromatic hydrocarbons suitable as charging stocks for our process areillustrative only.

Suitable xylene mixtures which can be used as charging stocks in ourprocess have been analyzed by A. D. Streiff and F. D. Rossini. Theseinvestigators have reported the results of analysis, by measurements offreezing points of appropriate mixtures, supplemented by analyticaldistillation, of the four individual C8 alkylbenzenes (ethyl benzene,o-xylene, m-xylene and p-xylene) occurring in the product from thefollowing five different catalytic petroleum refining processes: (1)Hydroforming," (2) two-pass fixed bed" catalytic cracking, (3)three-pass fixed bed catalytic cracking, (4) low-temperature fluid"catalytic cracking, and (5) high-temperat-re fluid" catalytic cracking.The data indicat that the relative amounts by volume of the four oralkylbenzenes are not greatly different in the five different products,being, on the average, as follows: ethylbenzene,12; o-xylene, 21;m-xylene, 48; p-xylene 19%. These amounts correspond substantially tothose called for in chemical thermodynamic equilibrium for the operatingtemperatures involved (J. Res. Nat. Bur. Standards 37, August 1946), p.117, Fig. 4) The naphthenlc plus paraflinic' hydrocarbon content of thesamples varied from about 7 to about 45 per cent by volume.(Alkylbenzenes in the Ca fraction from five different catalyticpetroleum refining processes, J. Res. Nat. Bur. Standards 39 (October1947), pp. 303-308.)

The disproportionation reaction may be effected in a system containingone liquid phase (homogeneous phase reaction) which contains at leastone mol of BF: combined per mol of xylenes in the isomerization reactionzone or in a' twoliquid system (heterogeneous phase reaction) when lessthan one mol of BF: is employed per mol of xylene charging stock in thereaction zone.

The following is an example which is adduced for illustrative purposesonly. The apparatus employed was a 1570 cc. carbon steel autoclavefitted with a 1725 R. P. M. mechanical stirrer. A

258 g. sample of a meta-xylene concentrate, 290 cc. of liquid hydrogenfluoride and 47 g. of BF:

were stirred in the reactor at 259 1 for minutes. At this temperaturethe reactor pressure was 270 p. s. i. g. The reactor was then cooled to75 F. and the HF and BF: were removed from the reaction mixture byvacuum distillation; The hydrocarbon product, which amounted to 96percent by weight of the charging stock, was fractionated in a columnpacked with wire gauze equivalent to theoretical plates and was found tohave the following composition:

Vol. Per Moi Per Cent Cent Tnlnann 22 26 xylenes 47 47 Trimethylbenzenes31 27 Mol Per Cent Product Equilib- Feed (0'8 Cut) rim 1 o-Xylene 1.317. 8 l7 m'Xylene 82. 3 56. 3 58 p-Xylene 13. 8 22. 3 23 Ethylbenzene 2.4 2. 4 2

I F. D. Rossini, Report on Chemical Thermodynamic Properties, A. P. I.Research Project 44, Mar. 31, 1947; Fig. 35.

Following the reaction, the products, or a fraction thereof, may besubjected to selective extraction with liquid hydrogen fluoride and BFs.We have observed that liquid hydrogen fluoride and BFa, when employed asa selective reaction solvent under appropriately selected operatingconditions effect the selective extraction of meta= xylene from thexylenes isomeric therewith. Although benzene and toluene have beenstated to form complexes with liquid HF and BFa, we have observed thatsuch complexes, if they are formed at all, are completely dissociated(i. a. they do not exist as such) at temperatures as low "as 0 C.

Also, when a solution of xylenes in liquid HF and BF: is treated towithdraw sufficient BF: to reduce its concentration below 1 mol per molof aromatic hydrocarbons contained in said solution, the solution can bereadily separated into two layers by conventional means such assettling, centrifuging or the like. Analysis of the tworesultant layersindicates that the xylene isomers are distributed in differentproportions in the two layers, viz., the raflinate" layer which ischaracterized by containing only small amounts of HE and BF: and whichconsists essentially of complex-free xylene isomers and the "extractlayer which consists of BBB-112E- xylene isomers dissolved in excessliquid HF. The distribution of xylene isomers in the rafflnate" andextract layers is essentially the same as would be produced by initiallycontactin the xylene with a molar excess of liquid HF and with BF: in anamount less than 1 mol per mol of xylenes. The withdrawal of BF: fromthe solution containing xylene can be effected by various methods whichwill be pointed out in some detail hereinafter.

The selective extraction process which we employ appears to functionthrough the formation of BF3HF-aromatic hydrocarbon complexes whichappear to be definite chemical compounds. A study of these complexes hasindicated that the aromatic hydrocarbon, particularly metaxylene orother xylene, and BFa are present in the complexes in equimolar ratio.The various BF3-HF-aromatic hydrocarbon complexes differ from each otherin their stability, a evidenced by the different partial pressure of BFxwhich is present over the different complexes at a given temperature.Our study of the BFa-HF-isnmeric xylene complexes has shown that therelative stability of the meta-, orthoand paraxylene complexes,respectively, is 20:2:1. We have further found that the relativestabilities of the complexes with the isomeric xylenes with BF: and HFcan be substantially correlated with the actual extractabilities of theindividual xylenes by liquid hydrogen fluoride and BFa.

We have also found that the selective extraction of a mixture of xyleneswith liquid hydrogen fluoride and BF: may be treated by the mathematicalmethods of analysis heretofore applied in the study of fractionaldistillation operations. The symbol, a, corresponds, in fractionaldistillation terminology, to the enrichment factor and equals the ratioof the relative volatilities of the components being distilled (or themolar ratio of a given component in the vapor phase to the othercomponents of the vapor phase divided by the molar ratio of the samecomponent in the liquid phase relative to the other components in theliquid phase). In extraction, the extract phase can be treated as thevapor phase and the raflinate as the liquid phase of distillation. Inour experimental work we have found that the alpha ratios of meta-,orthoand para-xylenes were 15.3:1.47:1 at 0 C., which is considered tobe good agreement with their stability equilibrium ratios of 2 0:2:1(supra) as determined by vapor pressure measurements of stirred forone-half hour at (iii-77 F. The initial reactor pressure was 350 p. s.i. g., but when stirring was started the pressure immediately fell to p.s. i. g., showing that the BF; was absorbed. At the end of the stirringperiod the mixture was allowed to settle, and the two phases wereseparated. The BF and BF: were removed from the extract phase by vacuumdistillation and the composition of the extract, as well as thecomposition of the railinate and the feed were determined byfractionation and by ultraviolet absorption analysis. The results of theexperiment are shown in the following table. The diiference incomposition between the raflinate and extract shows that meta-xylene wasselectively extracted by the HF-BFs.

TABLE Batch extraction of hydroformer xylenes with HF-BF:

REACTOR CHARGE Hydroformer xylenes, 239 g. (2.25 mols) BFs, 93 g. (1.4mols) HF, 354 g. (17.7 mols) RESULTS [Total hydrocarbon recovery=94 wt.percent-.1

Ultraviolet Absorption Analysis, Wt. Wt. Per Cent Wt., Per

Cent x X x Eth 1 yypyy lenc lene lene benzene Total Feed 239 100 19. 641. 2 16. 7 19. 7 97. 2 Rafllnate 95. 3 42. 26. 1 17. 7 23. 3 26. 1 93.2 Extract. 1%. 6 57. 5 19. 4 60. 7 12. 5 0.1 92. 7

Individual Hydrocarbon Balance, Wt. Per Cent Ortho- Meta- Para-Ethylbenzene Feed 1'9. 6 41. 2 16.7 19.1 Raiiinnte plus Extract 22. 343. 2 l7. 0 l1. 2 Balance +2. 7 +2. 0 +0. 3 8. 5

Fractionation Analysis of Products, Volume Per Cent Raflinate ExtractBenzene 2 0 0| Aromatics 98 83 C10 Aromatics 0 17 100 i 100 From thedata presented in the above table, it will be noted that 57.5% of thefeed, which is equivalent to 1.3 mols of xylenes, dissolved in theHF--BF3 and that 93 g. or 1.4 mols of BF: were used, which withinexperimental error is equal to the mols of xylenes present in theextract phase.

The single stage separation factor a of metaxylene is where N and N arethe moi fractions of metaxylene in the raflinate and extractrespectively. This is a very high separation factor and it can becalculated by the use of a McCabe-Thlele graphical analysis'that asystem of only four stages is needed to separate hydroformer xylenesinto an overhead product comprising orthoand para-xylenes and a bottomsproduct containing 95% meta-xylene. The distribution of orthoandpara-xylenes obtained in the present extraction is cons stent with a.values of 0.69 and 0.47. The 4: ratios of meta-, orthoand para-xylenesare, therefore, 15.3:1.47:1.

The individual hydrocarbon balance in the above table shows, withinexperimental error, that all three xylenes remained unchanged during therun; i. e., they neither isomerized nor disproportionated. However,there is a net disappearance of ethylbenzene and the results of thefractionation analyses of the products show that the ethylbenzene tendedto disproportionate to form benzene plus diethylbenzenes andethylxylenes. This disproportionation immensely simplifies the xyleneseparation problem since ethylbenzene is thereby removed far from theboiling range of the xylenes.

One illustrative embodiment of the process of this invention will bedescribed with reference to the accompanying figure. The xylene chargemay be a mixture consisting of the isomeric xylenes, ethylbenzene andassociated saturated hydrocarbons boiling in the range of about 270 to300 R, such as is conventionally produced in hydroforming processes.

The feed stocks to the initial extraction operation should besubstantially free of water, since water is tenaciously retained by bothHF and BFa. Conventional drying procedures may be used to treat the feedstocks. The xylenes charge is passed through valved line i0 intoextraction tower Ii. If desired a low boiling diluent may be introducedwith the xylene charging stock through valved line i2 in amounts betweenabout 0.1 and about 5 volumes (preferably about 0.8 to 1.5 volumes) pervolume of charging stock. Suitable diluents comprise low boilingsaturated hydrocarbons such as nor isobutane, pentanes, hexanes,heptanes, octanes; low boiling cyeloparaflinic hydrocarbons such ascyclopentane, methyland dimethylcyciopentanes, cyclohexane,methylcyclohexane; and the like. The extraction in tower I l isconducted in such a, manner that two immiscible phases are presenttherein, viz.. alower extract phase whose upper surface is indicated bymeniscus l3 and a supernatant raflinate phase it above meniscus l3. BF;and liquid hydrogen fluoride are introduced into the upper portion ofthe extraction tower through valved lines 15 and I6, respectively. Partor all of the diluent may be introduced (by lines not shown) directlyinto the extract phase below meniscus i3 in tower I I.

Although we prefer to employ essentially anhydrous hydrogen fluoride, i.e., HF containing not more than 1 to 2 weight percent of water, weemploy HF containing up to about 5 to 10 weight percent of water. By HF,as used herein, we intend to denote the molecular species having amolecular weight of 20 which weight is employed in the necessarycalculations.

' to employ about 1 mol of xylene contained in the charging stock andanaoeeprs Extraction tower II is provided with a manifold II to permitthe introduction of BF; at various levels in the extraction tower. Allor a portion of the HF and/or BF: may also be added to the chargingstock at a point or points in advance of the extraction tower II andadditional HF or BF: can then be added as described above. Extractiontower II is provided with a cooling coil or an equivalent suchas acooling jacket, l8, to remove the heat generated in theextractionoperation. Liquid meta-xylene reacts with liquid HF andgaseous BF: (one mol of each) to form a complex with the liberation of2.9 K cal. In order to improve the efliciency of contacting in tower H abed of a packing material l9 is provided. The packing material comprisesshaped solid fragments resistant to the action of HF and BFa, forexample, carbon. Monel metal, copper. certain magnesium-aluminum alloysand the like.

In the extraction tower the xylene charging stock is contacted with acounterflow of a molal excess of liquid hydrogen fluoride (between about5 and about 50 mols per mol of xylenes contained in said charging stock)and BF; in an amount between about 0.2 and about 0.8 mol per mol ofxylenes contained in said charging stock at a temperature between aboutF. and about 150 F. under pressure sufllcient at least to maintain theliquid phase, for a period of time sufllcient to eil'ect selectiveextraction, usually between about 1 and about 30 minutes. Usually it ispreferred BF: per mol of metaadditional amount of BF: equivalent toabout 0.5 molper mol o1 ethylbenzene contained in the charging stock. Ingeneral, our preferred extraction operation entails the employment ofbetween about 7 and about 15 mols oi! HF and between about 0.4 and about0.7 mol of BF; per mol of xylenes charging stock at a temperaturebetween about 60 F. and about 100 F. for a period of time between aboutand about minutes.

The raflinate phase derived from the selective meta-xylene extractionand ethylbenzene disproportionatlon operation is characterized by agreatly reduced content of meta-xylenes as compared with the amount ofmeta-xylene in the charging stock entering tower II. The raflinate istaken overhead from selective extraction tower H through valved line andheat exchanger 2| into stripping tower 22 provided with a reboiler coil23. Stripping tower 22 is operated at a to temperature between about 150F. and about 250 F. and a bottom tem erature between about 250 F. andabout 400 F.and a pressure between about 0 and about 100 p. s. i. g. toremove substantially all of the relatively small amounts of HF and BF;carried from tower I i by the raflinate phase. When a diluent isemployed in tower II it, too, will be stripped from the raflinate intower 22. The distillate passes overhead through line 24 and partialcondenser 25 into an accumulator and settling drum 26, from which BF: isdischarged overhead through valved line 21. A stratum of diluent iswithdrawn through valved side line 28 and liquid hydrogen fluoridesaturated with BF; is discharged through valved line 29. It will beobvious that all the eiiluents of drum 26 may be reemployed in thevarious extraction or isomerization-disproportionation operations.

Stripped raflinate hydrocarbons are discharged from tower 22 throughline 30 whence they pass through heat exchanger 3|. Since the dispro- 1through valved line 4| for recycle to extraction recycled through valvedline 30 to reflux tower 33 and the remainder diverted through valvedline 3 9. The tower bottoms consist essentially of a mixture oi orthoandpara-xyle'nes, possibly containing a small proportion of meta-xylene.The bottoms fraction in tower 32 is discharged through line 40, whence aportion may be passed tower l I. All or the remainder of the xylenebottom fraction from tower 33 is passed through valved line 42 intofractionating tower 43 provided with a reboiler coil 44. In tower 43 aparaxylene fraction is taken overhead through line 45 and condenser 46into accumulating drum 41.

' whence a portion is withdrawn through valved line 48 to reflux tower43 and the remainder is removed through valved line 49. A smallproportion of unconverted ethylbenzene may be present in the para-xylenefraction. In tower 43, the bottoms, consisting essentially ofortho-xylene. is withdrawn through valved line 50.

. An extract phase which is substantially enrichedin meta-xylene,relative to its concentration in the charging stock. is withdrawn fromtower ll through line II and is then passed through line Gland heatexchanger 54 into line 55, whence all or a portion may be divertedthrough valved line 56 into a stripper 51 which is operated undersimilar conditions to those prevailing in stripper 22. Stripper 51 isprovided with a reboiler coil 58. HF and BF: are taken overhead fromstripper 51 through valved line 59 for recycle to extraction or xylenedisproportionation. Low boiling saturated hydrocarbons such as propane,butanes, pentanes, etc. may be introduced into tower 51 to facilitatethe stripping operation. The bottoms in tower 58 comprise essentially ameta-xylene concentrate which also contains diethylbenzenes produced bythe disproportionation oi ethylbenzene in tower ll (mostlymeta-diethylbenzene) and ethylxylenes also produced in thedisproportionation reaction (predominantly 1-ethyl-3.5-dimethylbenzene).

The bottoms from tower 51 are removed through line 60, whence all or aportion is recyc ed to tower ll through valved line BI and cooler 62. Ifdesired, the stream passing through line 6! may be partially or whollydiverted by valved line 63 through heat exchanger 54 before passing intoheat exchanger 62. All or a portion of the bottoms from tower 51 may bediverted through valved line 64 into fractionatlng tower 65 providedwith reboiler coil 66. A meta-xylene fraction is taken overhead fromtower 65 through line 61 and condenser 68 into accumulator drum 69,whence a portion is recycled through" valved line 10 to reflux tower andthe remainder is passed into line II. From line H a portion of themeta-xylene fraction may be diverted through valved line 12 into line iifor recycle to the lower portion of tower II to backwash the extractphase therein. A substantial proportion of the meta-xylene fraction ispassed through valved line 13 as charge to the xylene disproportionationprocess to be described hereinafter.

11 The C aromatic hydrocarbons which accumulate as bottoms in tower 65may be discharged from time to time through a valved line.

If it is not desired to strip HF, BF: and C10 aromatic hydrocarbons fromthe concentrate of meta-xylene in liquid I-IF-BFa passing through line55, this stream may be wholly or partially diverted through valved line14 to pass to the xylenes disproportionation operation. From valved line14 the homogeneous solution of meta-xylene and small proportions oforthoand para-xylenes, in liquid HF-BFa, containing also some C10aromatic hydrocarbons produced by the disproportionation ofethylbenzene, is passed into line 15, thence through heat exchanger 16into line 11 and a reactor schematically represented at 18. A saturatedhydrocarbon diluent such as may be employed in extraction tower I I maylikewise be introduced by line 19 into line 80 in amounts between about0.2 and about 3 volumes per volume of hydrocarbon charging stock thereincontained. The diluent may be passed into reactor 18 through valved line19 which discharges into manifold 11.

The homogeneous concentrate of meta-xylene in liquid HF-BFa issubjected, in reactor 18, to a temperature between about 200 F. andabout 600 F., preferably about 250 F. to about 350 F. under a pressuresuflicient to maintain the liquid phase and for a period of timesufiicient to effect substantial xylenes disproportionation andisomerization, say, between about 2 minutes and about 4 hours.

When the reaction is conducted in homogeneous phase, the resultantreaction mixture is pref erably discharged from reactor I8 through line80, valve 8| and heat exchanger 82 into drum 83. In drum 83 suiilcientBF: is removed from the reaction products to reduce its concentrationbelow one mol per mol of xylenes and 09-010 aromatic hydrocarbonscontained in the reaction mixture. Preferably sufiicient BFLJ is ventedthrough line 84 and pressure control valve 85 to reduce theconcentration of BF: in the liquid in the drum to a value between about0.5 and about 0.75 mol per mol of xylenes and C9-Cl0 aromatichydrocarbons contained therein. Upon partial stripping of the BF: fromthe liquid contents of drum 83, the homogeneous liquid phase thereinseparates into two liquid phases, viz., a supernatant rafl1nate" phasewhich consists predominantly of orthoand para-xylenes, toluene andpossibly some pseudocumene and hemimellitene which flows over weir 86into the upper portion of settling drum 83, and a lower "extract phasewhich consists essentially of a solution of meta-xylene and Cs aromatichydrocarbons, principally mesitylene, in liquid HF and BF: which settlesinto the lower portion of drum 83.

The raflinate phase in drum 83 is withdrawn through valved line 81,whence it passes into stripper 22, whose operation has been describedabove, to be treated for the removal of HFv and BF: and for furthertreatment, if desired, in fractionating tower 33 and/or 43 to separateorthoand para-xylenes concentrates, respectively. Additionalfractionation facilities may be provided to separate toluene whichdistills with the paraxylene fraction and to separate C9 aromatics fromthe ortho-xylene bottoms in tower 43.

The extract phase in the lower portion of drum 83 may be withdrawnthrough valved line 88, heat exchanger 52 and manifold 11 for recycle toreactor 18. If desired, all or a portion of the stream passing throughline 88 may be diverted through a valved line into heat exchanger 82 asa heat conservation measure. Mesitylene is produced by xylenesdisproportionation in reactor 18 and 'will be present in the HFBF3solution in the lower portion of drum 83. The continued recycle ofmesitylene to reactor 18 with the stream in line 88 tends to prevent itscontinued formation, so that it is desirable to treat the stream in line88 from time to time, to remove its mesitylene con tent. This may beaccomplished by stripping off HF and BF: and fractionally distilling theresidual hydrocarbons into a Ca bottoms fraction and a xylenesdistillate, which distillate is then recycled to reactor 18.

An advantage of xylenes disproportionation in homogeneous liquid phaseis that little or no stirring is required to effect intimate contactingof the reactants and catalysts. However, heterogeneous (two immiscible)liquid phase disproportionation may be practiced in certain instances.Although more or less intensive stirring or agitation or other means ofcontacting is re-- quired in reactor 18 when two immiscible phases arepresent during reaction, this mode of operation has the advantage thatthe meta-xylene can be retained for the most part insolution in thecatalyst phase and the orthoand para-xylene isomerization products andtoluene, produced by xylenes disproportionation, are for the most partdscharged from the catalyst solution. The reaction mixture may then beconveniently discharged through line into drum 83 which in this mode ofoperation can serve simply as a settling-drum whence the meta-xylenesolution in liquid HFBF3 can be recycled through line 88 to reactor 18and a rafllnate layer withdrawn through line 81 for treatment ashereinbefore described. The BF: content of the HF-BFa-xyleries solutionpassing through manifold 11 may be suitably adjusted in order to obtaintwo liquid phases for heterogeneous-phase reaction by diverting at leasta portion of said stream through valved line 89 into a'stripper 90provided with a heating coil 9|. Sufficient BBB is withdrawn throughvalved line 82 to reduce the BFa concen-' tration in the solution tosubstantially less than 1 mol per mol of xylenes (and C10 aromatichydrocarbons); the partially strippedsolution is discharged from tower90 through line 93 whence it is forced by pump 94 into line 95 andthence into reactor 18.

If desired, the xylene charging stock may be passed into reactor 18without first being subjected to extraction in tower ll. Thus a xylenemixture containing ethylbenzene and saturated hydrocarbons may beintroduced through valved line 96 into line 15 and thence through heatexchanger 16 and manifold 11 into reactor 18. In this case it will benecessary to charge HF and BF: directly to the reactor, by valved lines91 and 98, respectively. When the xylenes charge containing ethylbenzeneis charged directly to reactor 18, ethylbenzene disproportionation andreaction with xylenes will accompany the isomerization anddisproportionation of xylenes and will yield benzene, diethylbenzenesand ethylxylenes as additional products. The reaction products may beprocessed in drum 83 as described above. However, a desirablealternative method of operation involves stripping HF and BF; from thereaction products, separation of aromatic hydrocarbons having molecularweights above and below xylene and, if desired, fractional distillationof the remaining xylenes mixture. To this end the eflluent from reactor18 is passed through line 80, valved line 93. valved line IIIII and heatexchanger IIII into stripper I02 provided with a reboiler coil I03,whence HF and BF; are removed overhead through valved line I04 and thestripped bottoms are discharged through valved line I into fractionatingtower II". A bottoms fraction comprising diethylbenzenes (predominantlymeta-), ethylxylenes (predominantly 1,3,5-) and mesitylene andpseudocumene is discharged through valved line I08, and a distillate I06provided with reboiler coil consisting essentially of benzene,

toluene and xylenes is passed overhead through line I09 and condenser 'II 0 into an accumulator drum III, whence a portion is returned throughvalved line I I2 as reflux to tower I08 and the remainder is dischargedthrough valved line II3 into fractionating tower II4 equipped withreboiler coil I I5. Mesitylene may be separated from diethylbenzenes andethylxylenes by further fractional distillation. In tower II4 adistillate boiling below the xylenes boiling range is taken overheadthrough line H6 and condenser III into an accumulator drum 8. Thisdistillate includes benzene, uent boiling below the xylenes boilingrange. A portion of condensate in accumulator drum II8 isrecycled totower II 4 through valved line .I I9

.and the remainder is discharged through valved line I20.

The bottoms in tower H4 consist essentially of a mixture or isomericxylenes which are removed through valved line I2I, whence they may beimpelled by pump I22 through line I23 into line I24, thence through heatexchanger I25 and line I23 toluene, and saturated hydrocarbondilapparent-to one skilled the extraction and 1 'tion.

into line In and extraction tower u to be wi l;

Jected to selective extraction with liquid hydrogen fluoride and BF: asdescribed above. Heat conservation may be effected by diverting at leasta portion of the stream flowing through line I24 through, valved lineI21 and heat exchanger I6. At least a portion of the xylene stream inline I23 is diverted through valved line I31 to reactor 18 to be furthersubjected to disproportionation.

If desired the isomeric xylene stream removed as bottoms fromfractionating tower II4 may be subjectedto further fractionaldistillation, being passed for this purpose from valved line I2I intovalved line I28 and thence into fractionating tower I23 equipped withreboiler coil I30. An ortho-xylene concentrate may be removed as bottomsfrom tower I29 through valved line I3I. A mixture of betaandpara-xylenes is removed overhead from tower I29 through line I32 andcondenser I33 into an accumulator drum I34,v

whence a portion is recycled to tower I29 as reflux through valved lineI35 and the remainder I is removed through valved line I 36 topump I22for recycle operation. If desired, the metaand para-xylene mixture inline I36 may be employed as a feed stock in reactor 18 or in anotherreactor.

If desired, especially where heterogeneous phase reaction is eifeeted inreactor 13, the product stream removed through lines 80 and 9,9 may bepassed directly into line I24 for return to extraction tower I I.

Although the accompanying flow diagram features the employment ofextraction towers, we may employ other conventional extractionequipment. For both extraction and isomerization and disproportionationoperations we may employ equipment heretofore employed in the alkylationof isoparaflins by olefins in the presence of liquid hydrogen fluorideor sulfuric acid.

Although the accompanying figure depicts apparatus which may be employedin continuous be employed and that the 14 processing it is apparent thatthe'p'rocess of our invention maybe operated in batch or semicontinuousequipment. Also it a plurality of extraction towers and reactors mayextraction and reaction may be eiiected in a plurality of stages.

It will be apparent that the equipment featured in the accompany ngfigure permits great flexibility of. operation and that numerouspermutations and combinations of process flow and operation sequencesare possible. These need not, however,- be detailed here as they willbereadily in the art. The above description has. accordinglmbeen devotedto a consideration of the primary process flows .through reaction unitsof this inven- By selective extraction, as used herein and in theappended claims is meant not only the process ofcontacting a mixture ofxylenes with added liquid hydrogen fluoride and BF: but also theprocessthat involves removing BF; from an HF'BFs-xylenes1 solution to producetwo immiscible liquid phases. v v

.The products of the present invention-can .be treated to remove smallresidual amounts of fluorine by convenional processes, such ascontacting with adsorbent carbon, active clays, alumina. bauxite, NaF orother alkali metal fluorides, aqueous solutions of caustic, etc. as iswell known in the art of defluorinating hydrocarbons. Although HF andespecially BF: are relatively expensive reagents and would of necessitybe recovered in any large commercial application of the process of thisinvention, in small scale operations the recovery of these reagentsmight be considered immaterial. When the recovery of HF and BF: as suchis not required, the distillation and stripping operations illustratedin the figure may be dispensed with. As an alternative to distillationof the extract phase, saidphase may be mixed with water, alkaline oracidic solutions or the like which dissolve the HF and BFa. leaving asupernatant hydrocarbon phase which may then be recovered andfractionated. A desirable acidic solution with which to treat theextract phase is the azeotropic HF-H2O solution,

which becomes enriched in HF upon contact with a the extract phase andfrom which the HF in excessof the azeotropic amount can thereafter bereadily recovered by distillation. An alternative would be to distillfree HF and BF: from the extract phase, following which the residualfirmly bound BFaI-IF-xylene and BFa--HFCa aromatic hydrocarbon complexcould be treated with water oraqueous alkaline 'or acidic solutionstoliberate xylene and C9 aromatic hydrocarbons bound in said complexes.In place of the aqueous solutions mentioned above, one may employorganic compounds capable of forming complexes with-HF and BF: and whichare capable of displacing xylenes, especially meta-xylene, mesitylene,m-diethylbenzene and ethylxylenes from their complexes with HF and BFa,e. g.,

- organic compounds having a more basic (greater will be apparent thatcompounds such as phenoLalkyl ethers, ketones,

aldehydes, etc.

Havingthus described our claim is:

1. A process which comprises contacting at least one xylene in theabsence of any substaninvention, what we tial proportion of benzene in areaction zone with between about 3 and about mols of liquid hydrogenfluoride per mol of said xylene and between about 0.01 and about 3 molsof BF: per mol of said xylenes at a temperature between about 250 F. andabout 600 F., under a pressure sufficient at least to maintain a liquidphase to produce a mixture of isomeric xylenes and to effectdisproportionation of a xylene to form toluene and mesityiene,subjecting the reaction products to selective extraction with liquidhydrogen fluoride in molar excess, based on total xylenes in saidreaction products, and with BF; in an amount between about 0.2 and about0.8 mol per mol of xylenes and mesityiene in said reaction products at atemperature between about 0 F. and about 150 F. under a pressuresuflicient at least to maintain a liquid phase, separating theextraction mixture into a liquid hydrocarbon layer substantiallyenriched in orthoand paraxylenes and toluene, and a solution ofmetaxylene and mesityiene in liquid hydrogen fluoride and BFa, andrecycling at least a portion of said hydrocarbon layer to said reactionzone.

2. The process of claim 1 wherein the temperature in said reaction zoneis between about 250 F. and about 350 F.

3. A process which comprises contacting at least one xylene in theabsence of any substantial proportion of benzene in a reaction zone withbetween about 3 and about 20 mols of liquid hydrogen fluoride per mol ofsaid xylene and between about 0.01 and about 3 mols of BF: per mol ofsaid xylene at a temperature between about 250 F. and about 600 F.,under a pressure sumcient at least to maintain a liquid phase to producea mixture of isomeric xylenes and to effect disproportionation of axylene to form toluene and trimethylbenzenes, subjecting the reactionproducts to selective extraction with liquid hydrogen fluoride in molarexcess, based on total xylenes in said reaction products, and with BF:in an amount between about 0.2 and about 0.8 mol per mol of xylenes andmesityiene in said reaction products at a temperature between about 0 F.and about 150 F. under a pressure sufficient at least to maintain aliquid phase, separating the extraction mixture into a liquidhydrocarbon layer substantially enriched in orthoand para-xylenes andtoluene and a. solution of xylenes and trimethylbenzenes in liquidhydrogen fluoride and BF; substantially enriched in meta-xylene andmesityiene with respect to said reaction products, separating ameta-xylene concentrate and a mesityiene concentrate, respectively, fromsaid solution, withdrawing said mesityiene concentrate from the process,and recycling at least a portion of said meta-xylene concentrate to saidreaction zone.

4. The process of claim 3 wherein the temperature in said reaction zoneis between about 250 F. and about 350 F.

5. A process which comprises contacting a hydrocarbon mixture comprisingmeta-xylene and at least one xylene isomeric therewith in the absence ofany substantial proportion of benzene in an extraction zone with liquidhydrogen fluoride in molar excess, based on total xylenes and with BF;in an amount between about 0.2 and about 0.8 mol per mol of totalxylenes at a temperature between about 0 F. and about 150 F. under apressure sufficient at least to maintain a liquid phase, separating theresultant mixture into a liquid hydrocarbon layer substantially enrichedin an isomer of meta-xylene and an HF 16 HF: solution of xylenessubstantially enriched in meta-xylene, with respect to the chargingstock to said extraction zone, subjecting said HI -BF;- xylenes solutionin a reaction zone to a tempera ture between about 250 F. and about 600F. under a pressure suflicient at least to maintain a liquid phase for aperiod of time suflicient to effect substantial disproportionation oixylenes, separating a xylenes fraction and xylene disproportionationproducts from reaction mixture and recycling at least a portion of saidxylenes fraction to said reaction zone.

6. The process of claim 5 which comprises the additional step ofrecycling a portion of said xylene fraction to said extraction zone.

'1. The process of claim 5 wherein the temperature in said reaction zoneis between about 250 F. and about 350 F.

8. A process for the disproportionation of a xylene which comprisescontacting a xylene in the absence of any substantial proportion ofbenzene in a reaction zone with liquid hydrogen fluoride in quantitysuffioient at least to form a distinct liquid phase and with BF; in anamount between about 0.01 and about 3 mols per mol of said xylene at atemperature between about 250 F. and about 600 F. under a pressuresuiflcient at least to maintain a liquid phase, passing at least aportion of the resultant reaction mixture to a settling zone,withdrawing a solution comprising xylenes and mesityiene in liquidhydrogen fluoride and BF; from said settling zone, separating HF and BFafrom the withdrawn solution and subjecting hydrocarbons thus derivedfrom said solution to fractional distillation to separate a xylenesfraction and a mesityiene-containing fraction, withdrawing saidmesityienecontaining fraction from the process, and recycling at least aportion of the last-named xylenes fraction to said reaction zone.

9. The process of claim 8 wherein the temperature in said reaction zoneis between about 250 F. and about 350 F.

10. A process for the production of mesityiene which comprisescontacting a xylene in the absence of any substantial proportion ofbenzene with liquid hydrogen fluoride in quantity sufiicient at least toform a distinct liquid phase and with at least about 0.5 mol of BF: permol of said xylene at a temperature between about 200 F. and about 600F. under a pressure sufficient at least to maintain a liquid phase andseparating a C9 fraction consisting essentially only of mesitylene fromthe reaction products.

11. A process for the production of mesityiene which comprisescontacting a xylene in the absence of any substantial proportion ofbenzene with liquid hydrogen fluoride in quantity sufficient at least toform a distinct liquid phase and with at least about 0.5 mol of BF-a permol of said xylene at a temperature between about 200 F. and about 600F. under a pressure sufficient at least to maintain a liquid phase,separating the reaction mixture into a predominantly hydrocarbon phaseand a predominantly acid phase and separating mesityiene from said acidphase.

12. The process of claim 11 wherein the re action temperature is about250 F.

13. The process of claim 11 wherein the reaction temperature is betweenabout 250 F. and about 350 F.

14. A process for the production of mesityiene which comprisescontacting a mixture of hydroformate xylenes in the absence of anysubstantial proportion of benzene with liquid hydrogen fluoride inquantity suflicient at least to form a distinct liquid phase and with atleast about 0.5 mol of BF; per mol of said xylenes at a tem- Peraturebetween about 250, F. and about 350 F. under a pressure sufllcient atleast to maintain a liquid phase, separating the reaction mixture into apredominantly hydrocarbon phase and a. predominantly acid phase andseparating mesitylene from said acid phase.

15. A process for the disproportionation of a xylene, which processcomprises contacting a xylene in the absence of any substantialproportion of benzene in a reaction zone with liquid hydrogen fluoridein quantity sufiicient at least to form a distinct liquid phase and withBF; in an amount between about 0.01 and about 3 mols per mol of saidxylene at a temperature at between about 250 F; andabout 350 F. under apressure suflicient at least to maintain a liquid phase, thereaftervaporizing a portion of the BF: from the resultant reaction mixture andseparating said reaction mixture by settling into a predominantlyhydrocarbon phase comprising essentially toluene and xylenes and apredominantly acid phase comprising essentially liquid hydrogen fluorideand an BI -BF: complex of mesitylene.

' 16. The process of claim 15 wherein at least about 0.5 'mol of BF: isemployed per mol of said xylene in said reaction zone.

17. A process for the production of mesitylene which comprisescontacting a xylene in the absence of any substantial proportion ofbenzene with liquid hydrogen fluoride in quantity suflicient at least toform a distinct liquid phase and with at least about 0.5 mol of BF: permol of said xylene at a reaction temperature of at least about 200 F.for a period of time suflicient to effect substantial disproportionationof said xylene under a pressure sufficient at least to maintain a liquidphase and separating a Ca fraction consisting essentially of mesitylenefrom the reaction products.

ARTHUR P. LIEN. DAVID A. McCAULAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. A PROCESS WHICH COMPRISES CONTACTING AT LEAST ONE XYLENE IN THEABSENCE OF ANY SUBSTANTIAL PROPORTION OF BENZENE IN A REACTION ZONE WITHBETWEEN ABOUT 3 MOLS OF ABOUT 20 MOLS OF LIQUID HYDROGEN FLUORIDE PERMOL OF SAID XYLENE AND BETWEEN ABOUT 0.01 AND ABOUT 3 MOLS OF BF3 PERMOL OF SAID XYLENES AT A TEMPERATURE BETWEEN ABOUT 250* F. AND ABOUT600* F., UNDER A PRESSURE SUFFICIENT AT LEAST TO MAINTAIN A LIQUID PHASETO PRODUCE A MIXTURE OF ISOMERIC XYLENES AND TO EFFECTDISPROPORTIONATION OF A XYLENE TO FORM TOLUENE AND MESITYLENE,SUBJECTING THE REACTION PRODUCTS TO SELECTIVE EXTRACTION WITH LIQUIDHYDROGEN FLUORIDE IN MOLAR EXCESS, BASED ON TOTAL XYLENES IN SAIDREACTION PRODCUTS, AND WITH BF3 IN AN AMOUNT BETWEEN ABOUT 0.2 AND ABOUT0.8 MOL PER MOL OF XYLENES AND MESITYLENE IN SAID REACTION PRODUCTS AT ATEMPERATURE BETWEEN ABOUT 0* F. AND ABOUT 150* F. UNDER A PRESSURESUFFICIENT AT LEAST TO MAINTAIN A LIQUID PHASE, SEPARATING THEEXTRACTION MIXTURE INTO A LIQUID HYDROCARBON LAYER SUBSTANTIALLYENRICHED IN ORTHO- AND PARAXYLENES AND TOLUENE, AND A SOLUTION OFMETAXYLENE AND MESITYLENE IN LIQUID HYDROGEN FLUORIDE AND BF3, ANDRECYCLING AT LEAST A PORTION OF SAID HYDROCARBON LAYER TO SAID REACTIONZONE.